XOR Neural Network gets stuck in training
One Neuron on its own can only solve linearly separable problems.
You need a combination of Neurons to solve non-linearly separable problems.
For the XOR case, you need at least 2 Neuron at the first layer, and 1 Neuron at the Output layer to properly classify it.
Keep in mind sometimes the 3 Neuron network might get stuck in a local minima as well, you will need some luck in the random initialization of weights.
Using the right seed during the random initialization of weights can help converge, and some other seed will only result in a stuck network.